Devices for monitoring tire pressure have been available for many decades, although the implementation of such devices in real-life applications has been rare. In recent years, however, as US Government legislation and consumer trends in automotive safety have driven the introduction of direct tire pressure monitoring systems, the design and manufacture of low cost, easily installed and vehicle systems-friendly devices have become key areas of development for automotive manufacturers and suppliers. Whereas some systems rely on visual indicators, the trend is towards systems that communicate wirelessly with a central vehicle operating system to provide real-time data to the vehicle operator. The concept of transmitting the information via wireless communications was conceived early and has now been adopted into many, if not all, modern tire pressure sensor systems (TPSSs). Such wireless systems require three main components: a means of sensing the tire pressure, a means of controlling the sensor and powering it up/down, and a radio transmitter/receiver.
Direct tire pressure monitoring systems are mounted with the pressure sensor inside or outside the tire of the vehicle and can be divided into three categories: i) systems that are attached to the wheel rim; ii) systems that are mounted on or in the tire itself; and iii) systems that are attached to the tire valve. Systems attached to the tire valve offer advantages in that they are easily installed and retrofitted and, if desired, the valve body can act as an antenna for the transmitter. Such systems, however, need to be as small and lightweight as possible. Otherwise, large locking systems are needed to retain the electronics and sensor in place and counterbalance weights are needed to keep the wheel in balance. For all three categories, increased size and weight relate directly to the increased failure rate of tire pressure monitoring systems during tire changes. Thus maintaining low size and weight are of great importance.
To keep the system small, manufacturers of tire pressure monitors have traditionally relied on providing a limited amount of information, related solely to the tire pressure, which is usually corrected for temperature by means of a temperature sensor. As tire pressure monitoring systems have become more sophisticated, however, the expectations of customers have increased, such that modern systems are expected to provide more features than a simple pressure reading, while maintaining a small format. Examples of additional features include providing tire location information and interrogation capability by a central module.
Manufacturers are resorting to a number of different approaches to achieve the desired functionality in a small format, either by combining individually packaged chips with separate functions into a module, or by increasing the level of integration in either the sensor or the integrated circuit (IC) or both. Such systems, however, still require multiple packages and additional components to achieve full functionality. Thus, many systems still rely on a bulky modular construction approach. Accordingly, there is a need in the art to develop a tire pressure sensor system that has the desired functionality, but is contained in a single small package.